FIGS. 3 and 4 show a typical conventional cooling apparatus for electrical equipment.
In these drawings, the reference number 21 indicates a heat sink of a control unit (not shown) such as an inverter. The heat sink 21 comprises a gate-shaped frame 24 having a flat section 22, with side sections 23 located respectively on both sides of the flat section 22, and fins 25. The frame 24 of the heat sink 21 is equipped with an electronic device (not shown) and thermally connected to a heating member. A cooling fan 26 is to be mounted to the frame 24 of the heat sink 21, and a fan guard 27 is to be mounted to the cooling fan 26 so as to cover the front face of the cooling fan 26 with a grille section 28 of the fan guard 27. The cooling fan 26 and fan guard 27 are formed with through holes 29 and 30 provided in corresponding positions, respectively. A long clamping screw 31 is respectively put through these through holes 29 and 30, and then screwed into a corresponding threaded hole (not shown) formed in the frame 24 of the heat sink 21 to fasten the cooling fan 26 and fan guard 27 to the heat sink 21.
The above-mentioned construction is cooled by the following manner.
A cooling airflow generated by driving the cooling fan 26 is directed into the interior of the frame of the heat sink 21. The cooling air is passed between fins 25 of the heat sink 21 and discharged to outside of the control unit and others. When the cooling air is passed between fins 25, heat exchange is performed between the fins 25 and the cooling air so that the heat sink 21, absorbing heat from the electronic device and others (not shown) drops in temperature. Thus, the electrical equipment including the control unit is cooled.
However, in the conventional cooling apparatus for electrical equipment, the following problems have been recognized.
(1) Inefficiency in utilizing the cooling air due to the circumvention of the cooling air through a side space of the cooling fan 26.
As shown in FIG. 4(a), when the cooling airflow generated by the cooling fan 26 flows between the fins 25 of the heat sink 21, a part of the cooling air comes in conflict with the front end of the fins 25 of the heat sink 21 so that a turbulence is caused in the cooling airflow.
In addition, between the cooling fan 26 and the heat sink 21, there exists a gap formed over the entire surface of the cooling fan 26 in its width direction at approximately the same position in the longitudinal direction of the cooling fan 26. Thus, the turbulent cooling air yields a kinetic energy in the width direction on the cooling fan 26, and can easily escape from the gap between the cooling fan 26 and the fins 25 through a side space of the cooling fan 26. Then, as shown by the arrow in FIG. 4(a), the cooling air escaping from the gap is turned over to an inlet port of the cooling fan 26, which results in inefficiency in utilizing the cooling air.
(2) Inefficiency in cooling due to high air resistance in the grille section 28 of the fan guard 27. Undesirable wind noise occurs in the grille section 28.
As shown in FIG. 4(b), the generated cooling airflow is directed on a tilt in the rotation direction of the cooling fan 26 with respect to a rotation axis of the cooling fan 26. Thus, when the cooling air is sucked toward the cooling fan 26, the cooling air obliquely passes through the grille section 28 of the fan guard 27 so that the air resistance of the grille section 28 is increased and the substantial airflow area of the grille section 28 is decreased, resulting in lowered efficiency in cooling. Further, each corner of the grille section 28 protrudes into the path of the cooling air so that the corner creates air turbulence to cause undesirable wind noise.
(3) Low efficiency and difficult assembly due to the fastening structure in which the cooling fan 26 and the fan guard 27 are commonly clamped to the heat sink 21 by the clamping screw 31.
As shown in FIG. 3, the cooling fan 26 and the fan guard 27 are commonly clamped and fastened to the heat sink 21 by the long clamping screw 31. Thus, the positioning of individual parts and the clamping of the clamping screw 31 are required to simultaneously operate, resulting in low efficiency and difficult assembly.
As a result, the effort required for periodical maintenance check and replacements for the cooling fan 26 inevitably deteriorates operational efficiency.